{"record":{"id":"1d593f9717e658a3","repo":"deepseek-ai/deepseek-harness","slug":"the-host-half-returned-undefined-did-you-forge","errorCode":null,"errorMessage":"the Host half returned `undefined` — did you forget `return`?","messagePattern":"the Host half returned `undefined` — did you forget `return`\\?","errorType":"exception","errorClass":"Error","httpStatus":null,"severity":"error","filePath":"packages/extensions/cordis-host-runner/src/index.ts","lineNumber":901,"sourceCode":"  private async startHost(\n    plugin: DynamicCordisPlugin,\n    hostCode: string,\n    run: DynamicCordisRun,\n  ): Promise<CordisErrorDetails | undefined> {\n    const handle = (method: unknown, fn: unknown): (() => void) => {\n      const normalized = normalizeHandler(method, fn)\n      run.handlers.set(normalized.method, normalized.handler)\n      const dispose = (): void => {\n        if (run.handlers.get(normalized.method) === normalized.handler) run.handlers.delete(normalized.method)\n      }\n      run.handlerDisposers.push(dispose)\n      return dispose\n    }\n    try {\n      const sandbox = createSandbox(plugin.pluginId, { handle })\n      const evaluated = await evaluateHostCode(sandbox, hostCode, plugin.pluginId, this.resolved.vmTimeoutMs)\n      if (!isPlugin(evaluated)) {\n        throw new Error(evaluated === undefined\n          ? 'the Host half returned `undefined` — did you forget `return`?'\n          : 'the Host half must return a Plugin function or an object with apply(ctx)')\n      }\n      run.fiber = await startHostHalf(\n        this.requireGroup(),\n        evaluated,\n        (error) => { this.steerGuardFailure(plugin, run, 'Host', errorDetails(error)) },\n      )\n      return undefined\n    } catch (error) {\n      for (const dispose of run.handlerDisposers.splice(0)) dispose()\n      return errorDetails(error)\n    }\n  }\n\n  private async settleActivation(\n    plugin: DynamicCordisPlugin | undefined,\n    resolution: DynamicCordisRunResolution,","sourceCodeStart":883,"sourceCodeEnd":919,"githubUrl":"https://github.com/deepseek-ai/deepseek-harness/blob/b150a551b8d465e31e418e1b2eaf5e79bbb7d28e/packages/extensions/cordis-host-runner/src/index.ts#L883-L919","documentation":"Error \"the Host half returned `undefined` — did you forget `return`?\" thrown in deepseek-ai/deepseek-harness.","triggerScenarios":"Thrown at packages/extensions/cordis-host-runner/src/index.ts:901 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"b150a551b8d465e31e418e1b2eaf5e79bbb7d28e","analyzedAt":"2026-08-24T18:12:29.105Z","schemaVersion":2},"datasetVersion":"2026-08-24T22:17:12.610Z"}